1. Field of the Invention
This invention relates to improvements in a latch device for a webbing anchor used in a seat belt system.
2. Description of the Prior Art
Seat belt systems of various types are adopted in automotive vehicles and the like, and the so-called passive type seat belt system is a typical example thereof. Among these seat belt systems, there is one of the type in which a portion of webbing is connected to an anchor movable along a guide rail and the anchor may be moved along the guide rail by a suitable driving member, whereby the webbing may assume a position in which it restrains the seat occupant or a position in which it does not restrain the seat occupant.
Now, when the anchor is moved toward one end of the guide rail and the webbing assumes the position in which it restrains the seat occupant, it is necessary that the anchor be held in that position. Otherwise, the anchor would move during the collision of the automotive vehicle, and the webbing could not completely restrain the seat occupant. As the reasons why the seat occupant cannot be restrained, there may be mentioned the following two cases: firstly, a case where the webbing moves to any other position than its regular position and becomes unable to restrain the seat occupant and secondly, a case where the anchor cannot completely receive the tension applied to the webbing and comes off (if there is only a slide rail, the anchor comes off the slide rail and may not receive the tension).
Therefore, in a seat belt system of the type in which an anchor is positioned at a vertical portion of a guide rail when a webbing is in a position in which it restrains a seat occupant, design is made such that an anchor bolt or the like receives the loads in longitudinal and lateral directions of a vehicle and latch means blocks vertical movement. On the other hand, in a seat belt system of the type in which an anchor is positioned at a horizontal portion of a guide rail when a webbing is in a position in which it restrains a seat occupant, design is made such that latch means blocks forward movement and an anchor bolt or the like blocks backward movement. In any case, however, the latch device of this type suffers from knotty problems.
That is, the latch device for the anchor must reliably lock the anchor during normal use and must quickly unlock the anchor during a desired time (when the seat occupant gets on and off the vehicle). Also, the anchor and the driving member for the anchor move near the face of the seat occupant along the guide rail and therefore are required to be compact and moreover move smoothly and with a small resistance. Furthermore, a latch member for locking the anchor is required to be compact and rigid. In contrast, the latch device for the anchor heretofore adopted includes a latch mechanism of complicated structure or the entire device is bulky and therefore, the anchor and its vicinity are complex in construction. When the anchor moves along the guide rail, that is, when the anchor passes a bending portion along the direction of movement of the vehicle body (hereinafter referred to as the "bending R portion") or a bending portion perpendicular to the direction of movement of the vehicle body (hereinafter referred to as the "camper portion"), the movement resistance becomes great, or smooth movement is hampered, and thus, it has been difficult to say that such latch device satisfies the above-mentioned requirements.